It's important to note that a blown fuse can be a symptom of a short circuit of internal wiring. The short-cut component and the fuse need to be replaced to fix the microwave oven completely.
Note:
There are microwave radiations and high voltage of the microwave oven. It is hazardous for anyone other than a professional person to carry out any service or repair operation that involves the removal of a cover that gives protection against exposure to microwave energy.